Not Applicable
Not Applicable
1. Field of the Invention
The present invention relates generally to pressure switches useful for monitoring vital process conditions in commercial and industrial fluid transport systems, and more particularly to a high-diagnostic, dual sensor process pressure switch having a one-out-of-two voting architecture.
2. Background of the Invention
In many commercial and industrial fluid transport systems, pressure switches are employed to measure the operational pressure of a process fluid disposed within the transport system. In particular, pressure switches are commonly used in sensitive fluid transport environments to detect hazardous process conditions, and to initiate the shut down of one or more process functions when a hazardous process condition is detected.
Generally, such pressure switches are disposed in an enclosed body that also houses an inert signal transfer medium, such as silicon, thereby effectively isolating the process fluid being measured from the pressure sensors. The housing therefore provides protection for the sensors from physical damage that could be directly caused by the process fluid. In this configuration, pressure is transmitted to the pressure sensor, via the transfer medium, through diaphragms located on the housing body that effectively separate the process fluid from the transfer medium while still permitting fluid pressures to be transmitted to the sensors.
Such pressure switches typically require verification of their operational stability at regular intervals to ensure accurate calibration and system functionality, especially in sensitive fluid transport applications. The most common calibration problems affecting presently known pressure switches are xe2x80x9cspan-shiftxe2x80x9d and xe2x80x9czero-shiftxe2x80x9d.
Span-shift occurs when the sensitivity of a pressure sensor is no longer accurate over an entire range of predetermined operational pressures. In contrast, zero-shift occurs when all of the pressure sensor readings are off by some constant error value within the required range. In some pressure sensors, zero-shift is much more likely to occur than span-shift; in certain other applications, span shift is more prevalent. Unfortunately, presently known pressure switches cannot generally detect either span-shift or zero-shift while a fluid transport system remains on-line. Instead, the switch must be removed from process service to validate calibration, requiring the transport system to be taken off-line, at least with respect to the particular process function being tested, and additional operation and maintenance personnel with appropriate testing equipment.
In order to overcome the aforementioned deficiencies in the prior art, it is an object of the present invention to provide a dual sensor pressure switch having a high-diagnostic, one-out-of-two voting architecture (hereinafter also referred to as xe2x80x9c1oo2Dxe2x80x9d) capable of detecting both span-shift and zero-shift in the sensors without first removing the pressure switch from process service, and without requiring additional personnel and testing equipment. A further object of the invention is to provide a plurality of bypass switches for the dual sensor circuits that will enable maintenance personnel to calibrate the circuits without removing the pressure switch from process service. A still further object of the invention is to provide a dual sensor pressure switch wherein when one of the sensors is operationally bypassed from the transport system, the process can continue to be monitored solely by the remaining on-line sensor, and wherein the ability to open the device""s switch output circuit is maintained even if one of the sensors fails entirely or is otherwise rendered ineffective.
A high-diagnostic, dual sensor pressure switch useful for monitoring process conditions in commercial and industrial fluid transport systems is provided, the pressure switch comprising a plurality of sensor circuits, each sensor circuit further comprising a pressure sensor, an analog-to-digital (hereinafter also referred to as xe2x80x9cA/Dxe2x80x9d) signal converter, a data processor or central processing unit, an output circuit, and an output switch; an analog signal comparator; and a diagnostics circuit further comprising an integrated diagnostics processor, a master diagnostics switch, and a plurality of servant diagnostics switches for preventing erroneous system shutdowns arising from a faulty pressure switch.